All things G1176 - the new "repost" thread.

[thecheat]

right on, thanks guys.

in that case,

THESE THINGS RULLZ>
\
Chris

 

[living sounds]

I've just realised the meter is working correctly on that unit. It's 'only' the audio path that doesn't get compresion. Changing the input, attack, release etc. results in correct meter behaviour. So this part of the circuit should be OK. I've triple checked all connecions and still found no error. Where to look? Does the unit still pass audio when the FET in the signal preamp is broken?

 

[ChrioN]

Having a small problem and couldn't find the answer to it, despite the improved search function...

When I turn on my unit, the needle gets to -2dB. It takes about 5 minutes or so for it to reach 0dB. Why is that? (This is in GR-mode)

Cleaning around the high impedance fet and other meter driver circuit related components seems to do the job descently.

 

[gswan]

I've just realised the meter is working correctly on that unit. It's 'only' the audio path that doesn't get compresion. Changing the input, attack, release etc. results in correct meter behaviour. So this part of the circuit should be OK. I've triple checked all connecions and still found no error. Where to look? Does the unit still pass audio when the FET in the signal preamp is broken?

Sounds like the GR FET is broken or inserted incorrectly.
In which case you can't possibly have biased it correctly.

 

[living sounds]

Sounds like the GR FET is broken or inserted incorrectly.
In which case you can't possibly have biased it correctly.

gswan,
the compressor had worked correctly for almost two years. It was biased correctly back then. Now it isn't working properly at all. But I just checked the FET by sending in a sinewave and measuring the voltages, and they change according to the GR shown by the meter. So the FET is working correctly. The sidechain signal seems to be all right, it just doesn't seem to reach the GR control amp. There might be a problem there, but I've measured the BC transistors in the section, and they all show the correct voltages...

 

[gswan]

Now measure the output of the GR amp and the FET Vgs and see that they are the same, whilst increasing the input signal to start compression. If your meter is showing compression GR operation, then the GR amp is probably working OK.

 

[user 37518]

Ok guys i already posted this, but since im new around here i thought of re-asking it here. My ratio board on my finished G1176 Mnats J rev is very weird. When im at 4:1 ratio, the threshold seems very low (input knob must be set very low otherwise it will start compressing like a mad man) but when i move to the upper ratio positions, for instance 12:1, the threshold seems higher and it compresses much less. This can also be observed on the ouput setting on the Meter. As i go higher on the ratio i have more output, as i go lower, i have less output. I checked all resistor values and wiring and it seems to be OK, also the rotary switch is a 5pos, 2 pol Alpha wired according to mnats pictorial. So what could be wrong??

 

[onlymeeee]

Ok guys i already posted this, but since im new around here i thought of re-asking it here. My ratio board on my finished G1176 Mnats J rev is very weird. When im at 4:1 ratio, the threshold seems very low (input knob must be set very low otherwise it will start compressing like a mad man) but when i move to the upper ratio positions, for instance 12:1, the threshold seems higher and it compresses much less. This can also be observed on the ouput setting on the Meter. As i go higher on the ratio i have more output, as i go lower, i have less output. I checked all resistor values and wiring and it seems to be OK, also the rotary switch is a 5pos, 2 pol Alpha wired according to mnats pictorial. So what could be wrong??

Nowt.  On an 1176, higher the ratio, higher the threshold.

 

[user 37518]

Ok guys i already posted this, but since im new around here i thought of re-asking it here. My ratio board on my finished G1176 Mnats J rev is very weird. When im at 4:1 ratio, the threshold seems very low (input knob must be set very low otherwise it will start compressing like a mad man) but when i move to the upper ratio positions, for instance 12:1, the threshold seems higher and it compresses much less. This can also be observed on the ouput setting on the Meter. As i go higher on the ratio i have more output, as i go lower, i have less output. I checked all resistor values and wiring and it seems to be OK, also the rotary switch is a 5pos, 2 pol Alpha wired according to mnats pictorial. So what could be wrong??

Nowt.  On an 1176, higher the ratio, higher the threshold.

Ohhh so the 4:1 setting should be compressing more than the 20:1 setting if they are at the same input level?

 

[living sounds]

Now measure the output of the GR amp and the FET Vgs and see that they are the same, whilst increasing the input signal to start compression. If your meter is showing compression GR operation, then the GR amp is probably working OK.

Did that, both FETS and the GR amp seem to be alright. They also roughly behave like the second half, which works OK. What else to check in this situation?

 

[Echo North]

[quote author=Dualflip]
Ohhh so the 4:1 setting should be compressing more than the 20:1 setting if they are at the same input level?
[/quote]

The threshold will be lower at 4:1 and therefor the GR will be higher...but the ratio will still be 4:1.  So at the same input/output you are getting a higher GR reading...but you are compressing at a lower ratio.

Look at Geoff's site:
http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=54%3A1176lnratios&option=com_content&Itemid=62

To determine that your ratios are right you have to test at least two levels below the threshold.

There are two things happening here...value of GR in db's and ratio of that compression against a bypassed signal.

Simplified example (hopefully I get this right):

Test point 1
Input/Output GR disabled = 6db
Output with 4:1 = 1db
Output with 20:1 = 2db

Test point 2
Input/Output GR disabled = 2db
Output with 4:1 = 0db
Output with 20:1 = 1.8db

With GR disabled the difference between the 2 points = 4db
at 4:1 = 1db (or 4:1 against GR disable)
at 20:1 = 0.2db (or 20:1 against GR disable)

Hope that makes sense...again read Geoff's page.

Mike

 

[user 37518]

Thankyou very much for the info ill check it out and ill get back to you, the only thing that bothers me, is that for example when im 4:1 in an X amount of input gain, my GR meter will display something like -10db of gain reduction, while on 20:1 with the input gain in the same position, wont even move a little bit from zero. Now for instance with a 0.775 signal feeding the compressor, when the pot is like 1/10 of its way (about -50db on the input pot engraving) on 4:1 mode the needle starts working, to do the same thing (the same GR) on 20:1 i have to lift the input pot to the half or even more like 2/3 CW (about -18 on the input pot engraving) thats the only thing that freaks me out.
Now that i mention this, i noticed a lot of other people that built the clone have a problem saying that the input gain is too hot, im using the NE5532 input stage (electronically ballanced), some solved this with the use of a T-attenuator, but i was thinking, instead of using a T-attenuator, if i used the Transformer option input with the transformer flipped backwards( 2:1) will this solve the excess of gain on the input?

 

[gyraf]

the only thing that bothers me, is that for example when im 4:1 in an X amount of input gain, my GR meter will display something like -10db of gain reduction, while on 20:1 with the input gain in the same position, wont even move a little bit from zero.

As mentioned before, the ratio switch also changes threshold - idea is that at some standard working levels, you can switch ratios and get approx. the same amount of GR - for instant comparison purposes. But measured at low levels, GR will be higher for low ratios - at very-high levels GR will be lower for low ratios.

Jakob E.

 

[gswan]

Did that, both FETS and the GR amp seem to be alright. They also roughly behave like the second half, which works OK. What else to check in this situation?

Well then I guess that unless the GR FET is not connected to the signal line on the Drain, then it's working OK.

 

[living sounds]

Well then I guess that unless the GR FET is not connected to the signal line on the Drain, then it's working OK.

The FET is not the problem. The GR amp is alright. Problem must be somewhere else.

Where does the actual compression of the audio signal happen? I've tried to understand the schematics, but I don't really get it (what are the things that look like broken bottles, never seen them before?). The GR amp is merely a DC signal, right? Can I shortcut it to the point where it affects the outgoing signal? To see if the problem is somewhere inbetween?

 

[MartyMart]

The FET is not the problem. I'm at a loss what to check...

Have you pulled the board out and checked for any "cold" solder joints in that area ?

MM.

 

[living sounds]

The FET is not the problem. I'm at a loss what to check...

Have you pulled the board out and checked for any "cold" solder joints in that area ?

MM.

Yes, I've even resoldered many connections just in case. The problem is my limited understanding of the compressor's topology. Am I correct in assuming that no actual audio signal runs through the GR amp, just a control signal? Where on the board does this control signal actually 'happen' to the audio signal?

 

[aku3351]

I can't find the Q-bias point, it seem been out of pot range...you have an idea of my problem?

 

[casrec]

  Quick question about my Sifam AL29, I read somewhere in here that you shouldn't use regulated voltage on the VU light. So should I tap into the Power transformers output rather than the VU pads on the MNATS Board. And if this is the case, should I ground off the PCB or take it to the same ground I am using for the AC inlet? Thanks for the help!

Brandon

 

[MartyMart]

Yes, I've even resoldered many connections just in case. The problem is my limited understanding of the compressor's topology. Am I correct in assuming that no actual audio signal runs through the GR amp, just a control signal? Where on the board does this control signal actually 'happen' to the audio signal?

Have a read through these articles for more detail on the topology of the "Fet" gain control circuits
than I could ever explain !  ( and some others )

http://www.tangible-technology.com/dynamics/comp_lim_ec_dh_pw2.html

Cheers,
Marty.